1. Technical Field
Controlling electric oil pumps in hybrid vehicles.
2. Background Art
A hybrid electric vehicle (HEV) typically includes an engine, such as an internal combustion engine (ICE), and an electric motor. For example, the HEV may be a series hybrid electric vehicle (SHEV), a parallel hybrid electrical vehicle (PHEV), or a parallel/series hybrid electric vehicle (PSHEV).
The series hybrid electric vehicle (SHEV) is a vehicle with an engine (most typically an ICE) connected to an electric machine, which provides electric power to a battery. Another electric machine called a traction motor is powered by the battery. The traction motor in the SHEV is the sole source of wheel torque. There is no mechanical connection between the engine and the drive wheels.
The parallel hybrid electrical vehicle (PHEV) has an engine (most typically an ICE) and an electric motor that work together to provide traction wheel torque to drive the vehicle. In addition, the motor in the PHEV can be used as a generator to recover regenerative power to charge the battery.
The parallel/series hybrid electric vehicle (PSHEV) has characteristics of both PHEV and SHEV configurations and is sometimes referred to as a “split” parallel/series configuration. In one of several types of PSHEV configurations, the engine is mechanically coupled to two electric machines in a planetary gear-set transaxle. A first electric machine, the generator, is connected to a sun gear. The engine is connected to a planetary carrier. A second electric motor, a traction motor, is connected to a ring (output) gear via additional gearing in a transaxle. Engine torque can power the generator to charge the battery. The generator can also contribute to the necessary wheel (output shaft) torque. The traction motor is used to contribute wheel torque and to recover regenerative braking energy to charge the battery. In this configuration, the generator can selectively provide a reaction torque that may be used to control engine speed.
During operation of a HEV, heat is generated and lubrication is needed for various components in the HEV. Thus, an engine-driven transaxle pump may be provided to cool and lubricate the various power transmission components in the HEV. However, when the HEV is being electrically operated, the engine is off and therefore the engine-driven transaxle pump is not operational. Therefore, an auxiliary electric pump may be implemented for purposes such as meeting the cooling and lubrication needs of the HEV when the engine is off.